The trigger for the warning is pretty straightforward; it looks at your recent posts and tries to guess whether or not if the question you're about to write will do well on the site. If your last post was poorly-received, it will warn you. If a significant % of your previous posts were poorly-received, it will warn you.
At a certain reputation level, the warning is disabled.
You fell into a bit of an edge-case, I suppose: your most recent questions were not particularly well-received... But also not particularly recent. We could avoid this with a cut-off date (a year maybe?) after which posts would no longer be considered; that said, it is fairly rare that someone in your situation encounters this warning.